Fourier transform Raman and DFT study of three annulated oligothiophenes with different molecular shapes.

Herein, we study the conjugation properties of three different thienoacenes, each of which has three or four fused thiophene rings, by means of Fourier transform Raman spectroscopy. The B3LYP/6-31G** vibrational analysis of all of the collected spectroscopic data evidences that the selective enhancement of a limited number of Raman scatterings is related to the occurrence in the three thienoacenes of a vibronic coupling between the lowest unoccupied frontier molecular orbital (LUMO) and some Raman-active skeletal nu(C==C) stretching modes of 1600-1300 cm(-1).     

Pesticide residue analysis of vegetables by gas chromatography with electron-capture detection

A new and original analytical method was developed for the routine analysis of 28 multiclass pesticide residues in vegetables (green pepper, red pepper, and tomato). The extraction was performed with acetone, and the pesticides were partitioned into ethyl acetate-cyclohexane (1 + 1, v/v). Residue levels in vegetables were determined by gas chromatography (GC) with electron-capture detection. Residue identities were confirmed by GC coupled with mass spectrometry in the selected ion monitoring mode. The average recoveries in pepper and tomato obtained for all analytes studied were 67.3 and 123.1%, respectively, with relative standard deviation between 1.8 and 7.0%. The detection limit for the pesticides studied varied from 0.1 to 2.6 microg/kg. The proposed method was applied to the analysis of these compounds in vegetables grown in experimental greenhouses.     

Calorimetric approach to tetronic/water interactions

Tetronic^®comprises X-shaped copolymers formed by four poly(propylene oxide) (PPO) andpoly(ethylene oxide) (PEO) block chains bonded to an ethylene diamine centralgroup. Micellization behaviour of three representative Tetronics (T304, T904and T1307) was characterized to gain an insight into the interactions betweenthe copolymer unimers and the state of water in their solutions. The enthalpyof demicellization, recorded at 37°C in an isoperibol microcalorimeter,indicated that the process was in all cases exothermic and the enthalpy rankedin the order T1307≥T904>>T304. Micellization is entropy-driven owing tohydrophobic interactions between the PPO chains.DSC analysisshowed that the crystallization and melting peaks of the free water remainingin T304 and T904 solutions were progressively shifted toward lower temperaturesas the surfactant proportion increased, owing to a colligative effect. Boundwater corresponded to 3 water molecules per EO repeating unit. In the caseof T1307, which has longer PEO chains, a splitting of the melting peak wasobserved, one peak appearing around 0°C due to free water and anotherat –15°C due to interfacial water. As T1307 proportion raised, theenthalpy of the former decreased, whilst the enthalpy of the latter increased.In 40% T1307 solutions, interfacial water overcame the proportion of freewater; there being 1 interfacial and 3 bound water molecules per EO repeatingunit. Gaussian deconvolution of FTIR spectra also enabled to characterizethe evolution of free water as a function of Tetronic proportion. The dependenceof micellization and water interaction behaviour on Tetronics structure shouldbe taken into account to use these copolymers as drug solubilizers and micellarcarriers.     

Asymmetric synthesis of rubiginones A(2) and C(2) and their 11-methoxy regioisomers

Convergent enantioselective syntheses of angucyclinone-type natural products rubiginones A(2) (2) and C(2) (1) and their 11-methoxy regioisomers 3 a and 3 b have been achieved by using two domino processes from a common enantiomerically pure 1-vinylcyclohexene 4. Key steps in the synthesis of this diene were the stereoselective conjugate addition of AlMe(3) on (SS)-[(p-tolylsulfinyl)methyl]-p-quinol (9) and the elimination of the beta-hydroxy sulfoxide fragment, after oxidation to sulfone, to recover a carbonyl group. The first domino sequence comprised Diels-Alder reaction with a sulfinyl naphthoquinone followed by sulfoxide elimination. An efficient opposite regioselection in the cycloaddition step was achieved in the convergent construction of the tetracyclic skeleton using a sulfoxide at C-2 or C-3 of the dienophiles 5 or 6, derived from 5-methoxy-1,4-naphthoquinone. The second domino process, triggered by oxygen and sunlight, allowed the transformation of the initial tetracyclic adducts into the final products after B ring aromatization, silyl deprotection and C-1 oxidation.     

Organocatalytic Enantioselective Synthesis of Pyrazoles Bearing a Quaternary Stereocenter

An efficient one‐pot asymmetric synthesis of pyrazoles bearing a chiral quaternary stereocenter has been developed. Quinine‐derived thiourea catalyzed the enantioselective addition of pyrazolones to isatin‐derived ketimines, providing the corresponding acetylated pyrazoles after in situ treatment with Ac₂O/Et₃N. The corresponding pyrazoles were afforded in high yields and excellent enantioselectivities.     

Platform Synthetic Lectins for Divalent Carbohydrate Recognition in Water

Biomimetic carbohydrate receptors (“synthetic lectins”) have potential as agents for biological research and medicine. However, although effective strategies are available for “all‐equatorial” carbohydrates (glucose, etc.), the recognition of other types of saccharide under natural (aqueous) conditions is less well developed. Herein we report a new approach based on a pyrene platform with polar arches extending from aryl substituents. The receptors are compatible with axially substituted carbohydrates, and also feature two identical binding sites, thus mimicking the multivalency observed for natural lectins. A variant with negative charges forms 1:2 host/guest complexes with aminosugars, with K₁>3000 m ^?1 for axially substituted mannosamine, whereas a positively charged version binds the important α‐sialyl unit with K₁≈1300 m ^?1.     

A new three-component domino synthesis of 1,4-dihydropyridines

Cerium ammonium nitrate (CAN) catalyzed the three-component domino reaction between aromatic amines, α,β-unsaturated aldehydes, and ethyl acetoacetate, providing an efficient new entry into 1,4-dihydropyridines. This new reaction requires very mild reaction conditions, has water as the only side product and is complementary to the classical Hantzsch synthesis in that it is well suited to the preparation of N-aryl-5,6-unsubstituted dihydropyridines. Experiments in the presence of a radical trap suggest that a one-electron oxidative mechanism can be excluded and that CAN acts as a Lewis acid.     

Rapid method for the determination of non-steroidal anti-inflammatory drugs in animal tissue by liquid chromatography-mass spectrometry with ion-trap detector

A rapid and new liquid chromatography-mass spectrometry with ion-trap detection method for the determination of meloxicam (MLX), flunixin meglumine (FLU), carprofen (CPF), and tolfenamic acid (TOLF) in animal tissue is described. MRLs between 10 and 500 microg kg(-1) in muscle and between 65 and 1000 microg kg(-1) in liver, from different animal species have been established in the EU for these compounds. After chemical hydrolysis, an organic extraction from homogenised tissue was performed. Final extract was injected in a liquid chromatograph with an ion-trap mass spectrometer with electrospray interface. Four identification points (one precursor and two product ions) and a minimum of one ion ratio was monitored for each compound. For quantitative purposes flunixin-D3 (FLU-D3) was used as internal standard. The method was validated using fortified blank muscle and liver from different animal species according to the 2002/657/EC European decision criteria. The decision limits (CCalpha) and detection capabilities (CCbeta) were determined and their values were at concentrations near the MRL for each substance.     

Simple and rapid determination of biogenic amines in wine by liquid chromatography-electrospray ionization ion trap mass spectrometry

A rapid liquid chromatographic-electrospray ionisation ion trap mass spectrometry (LC-ESI-ITMS) method has been developed for the routine analysis of eight of the most oenologically important biogenic amines in wine without any sample pre-treatment. The method involves addition of heptylamine as an internal standard (IS) and the direct injection of filtered wine samples previously diluted with ultra high purity (UHP) water. The full-scan MS-MS spectra and the identical retention times to those of reference standards were used for unequivocal identification of the analytes. For most amines, the most abundant ions were derived from the loss of an ammonia group, while in the case of spermine and the I.S. the major product ions arose from the loss of 1,3-propyldiamine and the production of adduct with water, respectively. Detection was achieved in positive ionisation with an ion trap mass spectrometer operating in multiple-reaction monitoring (MRM) mode. The method allowed accurate determination of the analytes in the range 0.5-40 ng mL⁻¹. Within-day and between-day relative standard deviation percentages were <8% and <12%, respectively. The overall process was successfully applied to identify and quantify biogenic amines in Rioja red wines. The new method is sensitive, rapid, cheap and less labour intensive.